That is, there is either the proper meaning in context (e.g. infringing copyright) which does not mesh with the common definition or there is the common definition (depriving somebody of property) which does not mesh with the context. People framing copyright infringement as "theft" want to take advantage of emotional connotations of the word in much the same way as people capitalizing on the fact that evolution is "just a theory".
I don't think anyone is claiming it doesn't hurt anyone (if everyone did it... etc), rather protesting against the fact that the copyright maximalist lobby has campaigned, with great success, to conflate two unrelated crimes in people's minds. (I'm not even going to touch the whole 'piracy' thing) I don't know about you, but I hate seeing people be played for fools.
Copyright infringement and stealing have about as much to do with each other as speeding and vehicular manslaughter.
It's like calling bullying 'murder'.
* (pirate) copy illegally; of published material
* (pirate) someone who robs at sea or plunders the land from the sea without having a commission from any sovereign nation
* (pirate) commandeer: take arbitrarily or by force; "The Cubans commandeered the plane and flew it to Miami"
Copyright infringement is just that, or 'unlawful copying' if you're afraid of longer words.
Considering how often Somalian criminals have been hijacking ships, and how this has been covered on pretty much every media form, I don't think there will be any confusion on this matter anytime soon.
Also, the verb form (Someone is pirating something) is in my experience almost exclusively used for copyright infringement. I've never heard of pirates pirating a shipment, but I've heard plenty of pirates pirating music.
I'm not saying you pirate (that's your business), more observing the disconnect between the argument ("it doesn't hurt anyone") and the tone ("but DON'T call it stealing!!")